A Holter monitor is a continuous tape recording of a patient's EKG for 24 hours. Since it is with patient during the patient's regular daily activities, it helps the physician correlate symptoms of dizziness, palpitations (a sensation of fast or irregular heart rhythm) or black outs. Since the recording covers 24 hours, on a continuous basis, Holter monitoring is much more likely to detect an abnormal heart rhythm when compared to the EKG which lasts less than a minute. It can also help evaluate the patient's EKG during episodes of chest pain, during which time there may be changes to suggest ischemia.